Known in the art is an internal combustion engine in which an NOx purification catalyst is arranged in an engine exhaust passage, a reducing agent feed valve for feeding a reducing agent upstream of the NOX purification catalyst is arranged in the engine exhaust passage, the NOX exhausted from the engine when fuel is burned under a lean air-fuel ratio is stored at the NOX purification catalyst, and when the air-fuel ratio of the exhaust gas should be made rich to release the stored NOX from the NOX purification catalyst, the combustion gas of a rich air-fuel ratio is generated in the combustion chamber or a reducing agent is injected from the reducing agent feed valve in accordance with the engine operating state (for example, see PTL 1). In this internal combustion engine, when the air-fuel ratio of the combustion gas in the combustion chamber is switched from lean to rich, when it is made rich, and when it is switched from rich to lean, a large amount of soot is produced and thereby there is a danger that the nozzle holes of the reducing agent feed valve is caused to clog by this large amount of produced soot. Therefore, in this internal combustion engine, in the interval from when the combustion is performed under a rich air-fuel ratio to when next combustion is performed under a rich air-fuel ratio, the reducing agent feed valve is made to inject a small amount of the reducing agent to blow off the soot deposited at the nozzle holes and thereby prevent the nozzle holes of the reducing agent feed valve from clogging.